1. Field of the Invention:
The present invention relates to a novel biologically active peptide of chicken which has a natriuretic action and a vasodepressor activity. More particularly, the invention relates to a process for isolating, identifying and utilizing a novel biologically active peptide which belongs to C-type natriuretic peptide.
2. Prior Art:
Recently, various peptides, which are known as natriuretic peptides (NP), have been identified and isolated from the atrium and brain of mammals. At present, these NPs can be classified into one of three types, A-type natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), on the basis of the homology of the primary amino acid sequences and the structures of precursors thereof.
Among them, ANP and BNP are also referred to as an atrial natriuretic peptide and a brain natriuretic peptide, respectively, since ANP and BNP were first isolated and identified from the atrium and brain, respectively (Matsuo, H. and Nakazato, H., Endocrinol. Metab. Clin. North Am., 16, 43, 1987; Sudoh, T. et al., Nature, 332, 78, 1988). However, it has turned out that ANP exists not only in the atrium but also in the brain, and BNP likewise exists not only in the brain but also in the atrium. Moreover, both ANP and BNP exhibit a natriuretic action and a vasodepressor activity. Therefore, it has been clarified that ANP and BNP respectively act as a hormone which regulates the homeostatic balance of body fluid volume and blood pressure of mammals, and at a neuro transmitter in the brain.
Whereas, CNP was isolated very recently from a porcine brain and characterized as a new type of NP which does not belong to any of ANP and BNP (Sudoh, et al., Biochem. Biophys. Res. Commun., 168, 863, 1990). CNP consists of 22 amino acid residues, and contains 2 cystein residues like ANP and BNP. Thus, the two cystein residues form an intramolecular disulfide bond, and the molecule has a cyclic structure consisted of 17 amino acid residues. Furthermore, the primary amino acid sequence constructing the cyclic structure of CNP was found to be highly homologous to those of ANP and BNP. The structure of CNP is characteristic in that it has no tail, while both ANP and BNP have a tail which consists of several amino acid residues added to the C-terminal of said cyclic structure. In other words, the C-terminal of CNP ends with a cystein residue. Thus, it has turned out that the structure of CNP differs from that of ANP or BNP in spite of the homology in other respects, and that CNP is a new type of NP since CNP exhibits a natriuretic action and a vasodepressor activity, and further shows a specific activity higher than ANP or BNP in relaxation of intestinum rectum specimens of chickens.
Therefore, it has been understood that various NP peptides, which can be classified into at least three different types, exist in mammals at present, and that these peptides participate in regulating the homeostatic balance of body fluid volume and blood pressure. Until now, details of CNP in terms of the distribution in the body and the physiological function were not as clear as in ANP and BNP.
On the other hand, the existence of NP peptides in non-mammal vertebrates has already been confirmed. Until now, however, only frog ANP, chicken NP and eel ANP have been isolated and characterized. The information about NP in non-mammals is less comprehensive than that for mammals (Sakata, J., Kangawa, K. and Matsuo H. Biochem. Biophys. Res. Commun., 155, 1338-1345, 1988; Miyata, A., Minamino, N., Kangawa, K. and Matsuo, H. Biochem. Biophys. Res. Commun., 155, 1330-1337, 1988; Takei, Y., Takahashi, A., Watanabe, T. X., Nakajima, K. and Sakakibara, S. Biochem. Biophys. Res. Commun., 164, 537-543, 1989).
The present inventors have already established a highly sensitive assay system of CNP by preparing a specific antibody toward CNP and developing a radioimmunoassay (RIA) system using the antibody (Japanese Patent Application No. 186583/90). Moreover, they found that a peptide (hereunder ir-CNP), exhibiting an immunological activity toward the anti-CNP antiserum, existed in chicken brains by searching for tissues of vertebrates other than mammal with the RIA system. Until now, however, isolation and characterization of a peptide belonging to CNP from aves have not been reported.